Lubricant compositions are widely used in devices with moving mechanical parts, in which their role is to reduce friction between the moving parts. This reduction may, in turn, reduce wear and tear and/or improve the device's overall performance. In many applications lubricant compositions also serve related and non-related supplemental purposes, such as reducing corrosion, cooling components, reducing fouling, controlling viscosity, demulsifying, and/or increasing pumpability.
Most lubricant compositions today include a base oil. Generally this base oil is a hydrocarbon oil or a combination of hydrocarbon oils. The hydrocarbon oils have been classified based on their composition and physical properties by the American Petroleum Institute as Group I, II, III or IV base oils. In order to further modify properties of the various base oils, so-called additive packages are frequently employed. Such may include materials designed to serve as antioxidants, corrosion inhibitors, antiwear additives, foam control agents, yellow metal passivators, dispersants, detergents, extreme pressure additives, friction reducing agents, and/or dyes. It is highly desirable that all additives be soluble in the base oil. Such solubility is preferably maintained across a wide range of temperature and other conditions in order to enable shipping, storage, and/or prolonged use of these compositions.
One class of additives that is of interest to lubricant formulators are polyalkylene glycols, or “PAGs.” Many PAGs are based on ethylene oxide or propylene oxide homopolymers, and are in some cases ethylene oxide/propylene oxide co-polymers. They often offer good performance and environmental properties, including good hydrolytic stability, low toxicity and biodegradability, desirable low temperature properties, and good film-forming properties.
Unfortunately, traditional PAGs, such as co-polymers of ethylene oxide (EO) and propylene oxide (PO) and homo-polymers of propylene oxide are often not soluble at treat levels of greater than 5 percent in the classical base oils. This led to the development of oil soluble polyalkylene glycols (OSP) which can be used as performance enhancing additives in hydrocarbon lubricants (see for example WO2011/011656). Two series of OSP products are commercially available. One series is based on co-polymers of PO and BO (butylene oxide) and a second series is based on homo-polymers of BO (polybutylene glycols). These offer excellent solubility in most Group I-IV base oils. A downside to these OSPs, however, is cost. In particular, BO containing OSPs are more expensive because butylene oxide, one of the starting materials for making the polymers, has high cost.
Therefore if a formulator would like to minimize his/her cost to manufacture of a hydrocarbon oil that contains a PAG then it would be more advantageous to use a PAG that comprises an OSP with a PO homo-polymer, a less expensive material, than one that contains an OSP alone.
The problem addressed by this invention is the provision of PAG compositions that contain cost effective PO homopolymers and that nevertheless provide improved properties, such as solubility, in hydrocarbon base oils.